Return temperature sensor error; furnace may cycle erratically or shut down with a code.

Safety first: Disconnect power before opening the furnace casing.

• Locate return NTC: Find the sensor on the return pipe entering the heat exchanger or hydraulic block.
• Inspect and clean connector: Unplug the sensor connector, check for corrosion or moisture, dry if needed, and reconnect firmly.
• Check cable routing: Ensure the cable is not pinched between panels or touching very hot surfaces that could melt insulation.
• Replace sensor if needed: If the error persists and wiring is intact, replace the return NTC with a genuine Roca part.

Warning: Incorrect sensor values can cause poor control and overheating; always use the correct replacement part.